1. Field of the Invention
The present invention relates to an imaging apparatus and an imaging mode control method.
2. Description of the Related Art
In an imaging apparatus in related art using a solid image pickup device such as a CCD (Charge Coupled Device), the quantity of light (light exposure) input into the image pickup device is adjusted by an aperture or electronic shutter speed. That is, when a bright scene is imaged, adjustments are made to reduce the light exposure so that so-called “overexposure” should not occur by an output signal of the image pickup device being saturated. Conversely, in a dark scene, adjustments are made to increase the light exposure so that so-called “underexposure” should not occur.
However, when a scene of high contrast is imaged (for example, backlight imaging or indoor/outdoor simultaneous imaging), there arises an issue described below. That is, due to an insufficient dynamic range of the solid image pickup device to be used, a bright portion is saturated to cause “overexposure” and “underexposure” is caused in a dark portion in which light exposure is insufficient by adjustments of light exposure alone so that it is difficult to properly reproduce both portions.
To solve this issue, a method of using two different electronic shutter speeds within a field has been developed (For example, see Japanese Patent Application Laid-Open No. 6-141229). According to this method, the electronic shutter speed is changed for each field to image information in a bright area and that in a dark area separately and each piece of the obtained information is combined into one image. As an application of the above method, an imaging apparatus (wide dynamic range camera) capable of picking up images in a wide dynamic range is known.
Two kinds of operating states of a wide dynamic range camera are generally known: a composite imaging mode in which wide dynamic range imaging is performed and a normal imaging mode in which wide dynamic range imaging is not performed. However, high contrast in images obtained from the composite imaging mode are frequently lost and it is known that if switched to the composite imaging mode in conditions of a small brightness difference, an unnatural image with reduced contrast of image is obtained. To improve such conditions, a method of automatically switching to the normal imaging mode in conditions of a small brightness difference and to the composite imaging mode in conditions of a great brightness difference has been developed (See, for example, Japanese Patent Application Laid-Open No. 2002-84449 (U.S. Pat. No. 5,455,621)).